In general, a conventional radiation sensitive electrical detector can be used in burglarproof, temperature sensing, illumination control and various monitor systems by means of specific circuit designs. The detecting angle of such detector is usually limited within 120.degree. degrees of the detector axis so that the detecting function of the detector is quite restricted.
In U.S. Pat. No. 3,923,382, Harding discloses a multifaceted mirror structure for infrared radiation detector, wherein each facet of the mirror is focused on a radiation sensing element. However, the mirror structure can only accomplish the focusing while the detecting angle range still can not be enlarged.